;*
; memmap.mac
;
;		Copyright (c) 2002 by Megan Gentry
;
; Abstract:
;	This program is designed to locate and report ranges
;	of memory in the low 64kb which can be referenced on
;	a PDP-11 and report them to the terminal.
;
;	The program was designed to be used to map the memory
;	on a proto desktop portable pdp-11 which only has a
;	4 line x 40 character LCD screen, which is why it
;	displays 3 lines and waits for character input to
;	proceed.
;-

	.asect
	. = 0

	reset				;reset the world
	br	start			; and jump to the code

	.word	nxmtrp			; : Address of NXM handler
	.word	340			; : PR7

	. = 300

start:	mov	#m.head,r0		;Announce us
	call	ttostr			; ...

	clr	r1			;R1 = Location under test
	mov	#2,r4			;R4 = Count of lines before wait

10$:	mov	r1,r2			;R2 = Low limit of memory range

; Here we look for the end of region of memory which exists
; (we assume that location 0 works)

20$:	clc				;Clear carry (NXM will set carry)
	tstb	@r1			;Test the location
	bcs	30$			;If it is non-existant...
	mov	r1,r3			;R3 = Hi limit of memory range
	inc	r1			;Update location under test
	bne	20$			; !loop!
	br	100$			;When we wrap in 64kb, we're done

30$:	call	report			;Report the range (R2,R3)

; Here we start looking for the start of the next region of
; responding memory.

40$:	clc				;Clear carry (NXM will set carry)
	tstb	@r1			;Test the location
	bcc	10$			;We've found memory...
	inc	r1			;Update location under test
	bne	40$			; !loop!
;	br	100$			;When we wrap in 64kb, we're done

100$:	call	report			;Report the range (R2,R3)

110$:	halt				;Stop the world...
	br	110$			; and don't let it restart...


report:	mov	r2,r0			;Print out region low address
	call	octout			; ...
	mov	#m.del,r0		;Print a delimiter
	call	ttostr			; ...
	mov	r3,r0			;Print out region hi address
	call	octout			; ...
	movb	#11,r0			;Another delimiter
	call	ttochr			; ...
	mov	r3,r0			;Determine number of words (octal)
	sub	r2,r0			; ...
	inc	r0			; ...
	call	octout			;Print it out
	mov	#m.crlf,r0		;On to next line
	call	ttostr			; ...
	dec	r4			;Should we delay a bit?
	bgt	10$			;Nope...
	mov	#m.pak,r0		;Yes, print out a prompt
	call	ttostr			; ...
	call	ttichr			;Get any character (where is that
					; found on a keyboard?)
	mov	#m.crlf,r0		;On to next line
	call	ttostr			; ...
	mov	#3,r4			;Reset the line count
10$:	return


octout:	mov	r0,-(sp)		;Save value
	bic	#177770,@sp		;Isolate an octal digit
	add	#^O60,@sp		;Make it printable
	ror	r0			;Shift right
	asr	r0			; three bits
	asr	r0			;  for next digit
	beq	10$			;If done... print out
	call	octout			;Not yet, recurse !!
10$:	mov	(sp)+,r0		;Print a digit
	call	ttochr			; ...
	return				;Unwind the stack and return


ttostr:	mov	r1,-(sp)		;Save R1 for awhile
	mov	r0,r1			;Save pointer to string
10$:	movb	(r1)+,r0		;Get a character of string
	beq	20$			;If null, add a <CR><LF>
	cmpb	r0,#200			;If a <200>, we're done
	beq	30$			; ...
	call	ttochr			;Print the character
	br	10$			; !loop!

20$:	movb	#15,r0			;output a <CR><LF> on a <NUL>
	call	ttochr			; ...
	movb	#12,r0			; ...
	call	ttochr			; ...
30$:	mov	(sp)+,r1		;Restore previously saved R1
	return


ttochr:	tstb	@#177564		;Terminal ready for output?
	bpl	ttochr			;Nope...
	movb	r0,@#177566		;Yes... output character
	return


ttichr:	tstb	@#177560		;Has a key been typed?
	bpl	ttichr			;Nope...
	movb	@#177562,r0		;Yes... get it...
	return


nxmtrp:	bis	#1,2(sp)		;Set PSW<C> for return
	rti				; from interrupt


m.head:	.asciz	/Memory Map:/
m.del:	.ascii	/ - /<200>
m.pak:	.ascii	/Press any key to continue.../<200>
m.crlf:	.byte	0
	.even

	.end